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1.
Opt Express ; 27(21): 29896-29904, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31684244

RESUMO

It has been proved that the detection of laser-induced breakdown spectroscopy (LIBS) could be improved by the flame. In this work, we applied flame enhanced LIBS for the detection of elements in water, while the flame was generated from the mixture of alcohol and aqueous solution. In the measurements, the flame is functioned as an assistance to enhance the LIBS detection, and also worked as a sampling way for the solution. The obtained results indicate that the detection of manganese, calcium, lithium and magnesium were significantly improved by the proposed method. It is found that the flame actually forms an environment for the laser-induced plasma to have higher temperature and lower electron density, as comparing with the plasma underwater. With the method, the quantitative analysis was tried out for the element of manganese, and the internal reference of calcium was used. It is interesting to find that, when mixing with the calcium, the minimum detectable concentration of manganese could be lowered and the intensity was greatly increased. According to the result, it is suggested that the proposed method might be a practical way for liquid detection of LIBS because of the simplicity and the effectiveness.

2.
Appl Opt ; 58(14): 3886-3891, 2019 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-31158203

RESUMO

The effects of salinity on underwater laser-induced breakdown spectroscopy (LIBS) were investigated with salinities ranging from 2‰ to 50‰. Both spectroscopic and fast imaging techniques were used to observe plasma emission. It was shown that as the salinity increased, emission intensities of the atomic lines increased, while intensities of the ionic lines were suppressed. The signal-to-background ratios of the spectral lines decreased as a function of salinity, but the signal-to-noise ratios changed irregularly with salinity. Image results demonstrated that brighter and longer plasma could be produced at higher salinity with higher plasma temperature and electron density. The calibration curves at different salinities indicated that the high salinity environment did not limit the detection capability of LIBS. The obtained results reveal the significant influences of salinity on underwater LIBS detection, which plays an important role in promoting applications of LIBS in the ocean.

3.
Appl Spectrosc ; 73(11): 1277-1283, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31117805

RESUMO

Laser-induced breakdown spectroscopy (LIBS) has been successfully applied to ocean exploration, but the changes in marine environmental factors could have an important impact on the LIBS signals. The aim of the research is to investigate the ambient water temperature effects on laser-induced plasma in bulk water. Both the spectroscopic and fast imaging techniques are used to observe the plasma emission with the temperatures in the range of 5-60 ℃. It is shown that as the ambient temperature increases, an obviously increasing trend of emission intensity is observed, both for the atomic and ionic lines of Ca. Higher plasma temperature and electron density can be obtained at higher ambient temperature. The image results demonstrate that hotter and larger plasmas can be produced in water with the increase of ambient temperature. In addition, it is found that the changes of plasma emission and morphologies could be related to the changes of physical property parameters of water such as thermal expansivity and viscosity with ambient temperature. The results suggest that the ambient temperature has great influences on laser-induced plasma, which needs to be taken into account in underwater LIBS measurement, especially on-site marine applications.

4.
Appl Opt ; 58(10): 2630-2634, 2019 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-31045063

RESUMO

In recent years, Raman spectroscopy techniques have been successfully applied to the area of deep-sea exploration. However, there are still some problems impeding the further application of Raman systems. For example, the large size of an underwater Raman system makes it difficult to deploy on the underwater vehicle. Meanwhile, the sensitivity is often a disadvantage, requiring improvement for detecting more trace components. To solve these problems, a new compact deep-sea in situ Raman spectroscopy system is presented in this paper. The whole system weighs 60 kg and is housed in an L800 mm×ϕ258 mm pressure vessel with an optical window on the front end cap. The main components include a 532 nm Nd:YAG laser, an optics module, a high-throughput spectrograph with 0∼4900 cm-1 spectral range and 8 cm-1 spectral resolution, a TEC-cooled 2000 pixel×256 pixel CCD detector, a PC104 embedded computer, and an electronics module. To evaluate the performance of the newly developed Raman system, systematic experiments have been carried out with solutions in laboratory, and the results have shown that the system limit of detection of SO42- is 0.4 mmol/L. The Raman system has been successfully deployed on a remote-operated vehicle on the Kexue research vessel in June 2015. The typical in situ detection results are presented in this paper, and it is shown that the Raman system is capable of detecting the Raman signal of SO42- and fluorescence of chlorophyll a (chl-a) and chromophoric dissolved organic matter (CDOM) in seawater. With 500 spectra accumulations and some data processing, the Raman signal of HCO3- is obtained. This is the first report of direct measurement of HCO3- by Raman system in in situ experiments. After further optimization, it is hoped to apply the Raman system in seafloor observation networks for long-time carbon cycling research.

5.
Sensors (Basel) ; 18(8)2018 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-30127236

RESUMO

In recent years, cabled ocean observation technology has been increasingly used for deep sea in situ research. As sophisticated sensor or measurement system starts to be applied on a remotely operated vehicle (ROV), it presents the requirement to maintain a stable condition of measurement system cabin. In this paper, we introduce one kind of ROV-based Raman spectroscopy measurement system (DOCARS) and discuss the development characteristics of its cabin condition during profile measurement process. An available and straightforward modeling methodology is proposed to realize predictive control for this trend. This methodology is based on the Autoregressive Exogenous (ARX) model and is optimized through a series of sea-going test data. The fitting result demonstrates that during profile measurement processes this model can availably predict the development trends of DORCAS's cabin condition during the profile measurement process.

6.
Appl Opt ; 57(13): 3539-3545, 2018 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-29726528

RESUMO

Laser-induced breakdown spectroscopy (LIBS) is a new technique for seashell elemental analysis, and now that application is in rapid development. In this work, LIBS was applied for scallop shell [Chlamys (Azumapecten) farreri] analysis using the element ratio Sr/Ca, and the analytical result was compared under objective lens (OL) focusing and single lens (SL) focusing, respectively. It is interesting to find that, under the two focusing arrangements, the ratio (Sr/Ca) variation on the shell cross section performed completely differently, while in technical aspects, the two focusing arrangements presented almost the same characteristics in a standard sample. Also, the seashell annual growth could be well indicated by high values of Sr/Ca intensity ratio when using OL, but under SL focusing no pattern was found. The difference of shell sampling amount and size might be the reason for inconsistent analysis performance under the two focusing arrangements. The scanning electron microscopy (SEM)-energy dispersive spectrometer (EDS) scanning results of the shell proved that LIBS analysis under OL focusing was closer to the actual Sr/Ca distribution than that under SL focusing. The obtained results might be useful for the methodology of LIBS in seashell applications.


Assuntos
Exoesqueleto/química , Cálcio/análise , Lasers de Estado Sólido , Pectinidae , Análise Espectral/métodos , Estrôncio/análise , Animais
7.
Appl Opt ; 57(7): 1640-1644, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29522012

RESUMO

Laser-induced breakdown spectroscopy (LIBS) has drawn more attention as a new technique for in situ detection of seawater, especially for hydrothermal areas. In order to evaluate the focusing geometry effect on laser-induced plasma in bulk water, four focusing arrangements were tried out with a single lens as well as with a double-lens combination. We demonstrated that, for the same transmission distance in water, the double-lens combination with shorter effective focal length generated more condensed plasma, as shown by the spectroscopic and fast imaging results. Accordingly, the moving breakdown phenomenon significantly decreased with well-improved LIBS intensity, signal-to-noise ratio, and stability. The plasma emissions evidently attenuated along the laser transmission due to the strong absorption effect of the water medium. Based on the acquired results, the performance of a practical detection window was evaluated by combining the regular lens with a customized lens-shaped optical window, and a positive outcome was also reached. The obtained results suggested that improved LIBS detection could be easily achieved via settling another lens window to LIBS system, which is considered helpful for better in situ submarine application.

8.
Sensors (Basel) ; 17(12)2017 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-29194357

RESUMO

Raman spectroscopy has great potential as a tool in a variety of hydrothermal science applications. However, its low sensitivity has limited its use in common sea areas. In this paper, we develop a near-concentric cavity-enhanced Raman spectroscopy system to directly detect bicarbonate in seawater for the first time. With the aid of this near-concentric cavity-enhanced Raman spectroscopy system, a significant enhancement in HCO3- detection has been achieved. The obtained limit of detection (LOD) is determined to be 0.37 mmol/L-much lower than the typical concentration of HCO3- in seawater. By introducing a specially developed data processing scheme, the weak HCO3- signal is extracted from the strong sulfate signal background, hence a quantitative analysis with R² of 0.951 is made possible. Based on the spectra taken from deep sea seawater sampling, the concentration of HCO3- has been determined to be 1.91 mmol/L, with a relative error of 2.1% from the reported value (1.95 mmol/L) of seawater in the ocean. It is expected that the near-concentric cavity-enhanced Raman spectroscopy system could be developed and used for in-situ ocean observation in the near future.

9.
Appl Opt ; 56(29): 8196-8200, 2017 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-29047684

RESUMO

The exploitation and research of deep-sea hydrothermal vent has been an issue of great interest in ocean research in recent years. Laser-induced breakdown spectroscopy (LIBS) has great potential for ocean application due to the capabilities of stand-off, multiphase, and multielement analysis. In this work, a newly developed compact 4000 m rated LIBS system (LIBSea) is introduced with preliminary results of sea trials. The underwater system consists of an Nd:YAG single-pulsed laser operating at 1064 nm, an optical fiber spectrometer, an optics module, and an electronic controller module. The whole system is housed in an L800 mm×ϕ258 mm pressure housing with an optical window on the end cap. It was deployed on the remote operated vehicle Faxian on the research vessel Kexue, and in June 2015 was successfully applied for hydrothermal field measurements at the Manus area. The obtained results are shown that the LIBS system is capable of detecting elements Li, Na, K, Ca, and Mg in the hydrothermal area. Profiles of LIBS signals of elements K and Ca have also been obtained during the sea trial. The results show that the K emission line is gradually broadened with depth from sea surface to sea floor (1800 m or so); the K intensity shows a hump shape with maximum value at about 1050 m. The Ca emission line is rapidly broadened below 400 m and slowly narrowed to the sea floor; the Ca intensity shows no obvious change below 400 m and increases continuously to sea floor. A very interesting finding is that the small fluctuations of intensity profile curve of Ca show a degree of correlation with seawater temperature change. The sea trial results prove the performance of LIBSea. After further optimization, it is hoped to apply the LIBS system to the in situ mineral deposits and hydrothermal vent fluid detection in deep sea.

10.
Appl Opt ; 55(27): 7744-8, 2016 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-27661606

RESUMO

The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. As a potential technique for oceanic applications, Raman spectroscopy has already proved its advantages in the simultaneous detection of multiple species during previous deep-sea explorations. Due to the low sensitivity of conventional Raman measurements, there have been many reports of Raman applications on direct seawater detection in high-concentration areas, but few on undersea dissolved gas detection. In this work, we have presented a highly sensitive Raman spectroscopy (HSRS) system with a special designed gas chamber for small amounts of underwater gas extraction. Systematic experiments have been carried out for system evaluation, and the results have shown that the Raman signals obtained by the innovation of a near-concentric cavity was about 21 times stronger than those of conventional side-scattering Raman measurements. Based on this system, we have achieved a low limit of detection of 2.32 and 0.44 µmol/L for CO2 and CH4, respectively, in the lab. A test-out experiment has also been accomplished with a gas-liquid separator coupled to the Raman system, and signals of O2 and CO2 were detected after 1 h of degasification. This system may show potential for gas detection in water, and further work would be done for the improvement of in situ detection.

11.
Sensors (Basel) ; 16(9)2016 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-27563899

RESUMO

In hope of developing a method for oil spill detection in laser remote sensing, a series of refined and crude oil samples were investigated using time-resolved fluorescence in conjunction with parallel factors analysis (PARAFAC). The time resolved emission spectra of those investigated samples were taken by a laser remote sensing system on a laboratory basis with a detection distance of 5 m. Based on the intensity-normalized spectra, both refined and crude oil samples were well classified without overlapping, by the approach of PARAFAC with four parallel factors. Principle component analysis (PCA) has also been operated as a comparison. It turned out that PCA operated well in classification of broad oil type categories, but with severe overlapping among the crude oil samples from different oil wells. Apart from the high correct identification rate, PARAFAC has also real-time capabilities, which is an obvious advantage especially in field applications. The obtained results suggested that the approach of time-resolved fluorescence combined with PARAFAC would be potentially applicable in oil spill field detection and identification.

12.
Guang Pu Xue Yu Guang Pu Fen Xi ; 36(2): 445-8, 2016 Feb.
Artigo em Chinês | MEDLINE | ID: mdl-27209747

RESUMO

The Laser-induced fluorescence spectra combined with pattern recognition method has been widely applied in discrimination of different spilled oil, such as diesel, gasoline, and crude oil. However, traditional three-dimension fluorescence analysis method, which is not adapted to requirement of field detection, is limited to laboratory investigatio ns. The development of oil identification method for field detection is significant to quick response and operation of oil spill. In this paper, a new method based on laser-induced time-resolved fluorescence combined with support vector machine (SVM) model was introduced to discriminate crude oil samples. In this method, time-resolved spectra data was descended into two dimensions with selecting appropriate range in time and wavelength domains respectively to form a SVM data base. It is found that the classification accurate rate increased with an appropriate selection. With a selected range from 54 to 74 ns in time domain, the classification accurate rate has been increased from 83.3% (without selection) to 88.1%. With a selected wavelength range of 387.00~608.87 nm, the classification accurate rate of suspect oil was improved from 84% (without selection) to 100%. Since the detection delay of fluorescence lidar fluctuates due to wave and platform swing, the identification method with optimizing in both time and wavelength domains could offer a better flexibility for field applications. It is hoped that the developed method could provide some useful reference with data reduction for classification of suspect crude oil in the future development.

13.
Guang Pu Xue Yu Guang Pu Fen Xi ; 36(1): 259-61, 2016 Jan.
Artigo em Chinês | MEDLINE | ID: mdl-27228778

RESUMO

Spectroscopic sensor is becoming an important issue for the deep-sea exploration due to the advantages of multi-specie, multi-phases and stand-off detection. Different approach have been developing in recent years based on LIBS (Laser Induced Breakdown Spectroscopy) and Raman spectroscopy since Raman-LIBS are complementary techniques with the similar components and the capability of molecular and elementary analysis. In this work, we built a LIBS-Raman system and detected Na2SO4 in aqueous solution to evaluate the potential ocean application. With the same laser, spectrometer and detector, a hybrid of Raman and LIBS system was developed to realize the detection of anions and cations in the seawater. The optics was composed by two parts. Raman channel and LIBS channel, and the signal was collected by a Y type optical fiber bundle. The signal from two channels was separated by imaging on different arrays of the CCD detector. The Raman spectra of SO4(2-) and LIBS spectra of Na was successfully detected simultaneously when the pulse energy was above 3.6 mJ. However, due to the strong bremsstrahlung radiation of LIBS, the signal to noise ratio of Raman was significantly decreased as the laser energy increasing. The results manifested the great potential of Raman-LIBS combination for the underwater detection.

14.
Guang Pu Xue Yu Guang Pu Fen Xi ; 36(4): 1186-90, 2016 Apr.
Artigo em Chinês | MEDLINE | ID: mdl-30052344

RESUMO

Laser-induced breakdown spectroscopy (LIBS), as a promising in-situ underwater detection technology, has received extensive attention in the field of ocean exploration. Improving the remote sensing ability of LIBS is crucial in bringing this technology into practical applications, hence higher laser energies, i.e. over threshold, are required. To characterize the plasma induced with super threshold energies and have a better understanding of resulted moving breakdown process, some extensive investigations into KCl water solution have been carried out with spectra-image jointed analysis. The spatial span and the brightest spot position of plasma radiation, with different laser energies from 1 to 20 mJ, were determined from the recorded plasma images. It was found that the plasma stretched from 0.49 to1.83 mm, as the laser pulse energy increased from 1 to 20 mJ, with a center position shift of 0.79 mm towards the incident laser beam. The obvious power dependence has also been observed from the obtained spatial resolved atomic spectra. Although the axial distributions at different energies were similar, both the position and the intensity of potassium atomic emission maximum varied. The optimal laser energy was determined to be 5 mJ with the emission intensity maximum higher than that at any other investigated energies. The obtained results suggested that the power dependence of atomic emission should be taken into account on increasing laser energy to meet the needs of stand-off LIBS applications. The FWHM and signal to background ratio of K Ⅰ 769.90 nm under different laser energies have also been investigated.

15.
Guang Pu Xue Yu Guang Pu Fen Xi ; 35(8): 2339-42, 2015 Aug.
Artigo em Chinês | MEDLINE | ID: mdl-26672321

RESUMO

The peaks' overlapping often exists in Raman spectroscopy analysis, because of the low spectral resolution of the spectrograph and the complex sample components. The overlapped peaks lead to the errors in peak parameters extraction easily, and at last lead to the analysis error of sample components, which increases the difficulty in automatic analysis of field spectra. The identification of overlapped peaks is the key difficulty of in-situ spectra analysis. To solve this problem, an automatic method of identifying the overlapped peaks was established basing on an analysis model with multiple Gaussian shape peaks. The peak number and the initial parameters(the peak position, peak height, and width) were obtained by symmetric zero-area transformation firstly, and then the parameters were optimized by Levenberg-Marquardt fitting method eventually. Some algorithm experiments were executed to test the method respectively by simulated data and Raman spectra data, and the former showed that the symmetric zero-area transformation method can extract the initial peak parameters with high accuracy, and then converges fast, and is adaptive to signal with wide dynamic range of SNR, but has false and omissive peaks to low SNR signal. The research results show that the automatic method of identifying the overlapped peaks with symmetric zero-area transformation combined with L-M fitting has a certain practical value.

16.
Guang Pu Xue Yu Guang Pu Fen Xi ; 35(6): 1582-6, 2015 Jun.
Artigo em Chinês | MEDLINE | ID: mdl-26601371

RESUMO

To evaluate the feasibility of laser induced time-resolved fluorescence technique for in-situ detection of underwater suspended oil spill, extensive investigations have been carried out with different densities of crude oil samples from six different wells of Shengli Oilfield in this work. It was found that the fluorescence emission durations of these crude oil samples were almost the same, the Gate Pulse Delay of DDG (Digital Delay Generator) in the ICCD started at 52ns and ended at 82ns with a width (FWHM) of 10 ns. It appears that the peak location and lifetime of fluorescence for different crude oil samples varied with their densities, and those with similar densities shared a similar lifespan with the closer peak locations of fluorescence. It is also observed that the peak of fluorescence remained the same location before reaching the maximum intensity, subsequently shift to longer wavelength as fluorescence attenuated from maximum intensity with a red shift among 17-30 nm varied with samples. This demonstrated that the decay rate of fluorescent components in the crude oils was different, and energy transfer between these components might exist. It is hoped that those obtained results and characteristics could be the useful information for identification of suspended spilled-oil underwater.

17.
Appl Spectrosc ; 69(12): 1412-6, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26556043

RESUMO

In this paper, by means of Cu(2+) converting to Cu, the sub-ppb detection of copper in aqueous solution was successfully achieved using laser-induced breakdown spectroscopy (LIBS), and the sensitivity was found depending on the voltage applied for the deposition. With increasing voltage, the minimum detectable concentration was significantly lowered, while the signal intensity instability was increased. In order to reduce the impact from the intensity fluctuation, an estimation method was developed to determine the copper concentration via comparing minimum detectable concentrations. The obtained results suggest this method is a potential way toward quantitative analysis.

18.
Guang Pu Xue Yu Guang Pu Fen Xi ; 35(3): 645-8, 2015 Mar.
Artigo em Chinês | MEDLINE | ID: mdl-26117872

RESUMO

The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. Raman spectroscopy has a great advantage in simultaneous multiple species detection and is thus regarded as a favorable choice for ocean application. However, its sensitivity remains insufficient, and a demand in enhancements is called! for before putting Raman spectroscopy to actual use in marine studies In this work, we developed a near-concentric cavity, in which laser beam could be trapped and reflected back and forth, for the purpose of intensifying Raman signals. The factors that would influence Raman signals were taken into account. The result show that the smaller angle between collection direction and optical axis of reflection mirror, the stronger the signal and signal to noise ratio (SNR) is. With a collection angle of 30 degrees, our Near-concentric Cavity System managed to raise the SNR to a figure about 16 times larger than that of common methods applying 90 degrees. Moreover, the alignment pattern in our system made it possible to excel concentric cavity with a 3 times larger SNR. Compared with the single-pass Raman signal, the signal intensity of our near-concentric cavity was up to 70 times enhanced. According to the obtained results of CO2 measurement, it can be seen that the new system provides a limit of detection(LOD) for CO2 about 0.19 mg x L(-1) using 3-σ criterion standard, and the LOD of 11.5 µg x L(-1) for CH4 was evaluated with the theoretical cross section values of CO2 and CH4.

19.
Sensors (Basel) ; 15(6): 12377-88, 2015 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-26016919

RESUMO

The levels of dissolved sulfate and methane are crucial indicators in the geochemical analysis of pore water. Compositional analysis of pore water samples obtained from sea trials was conducted using Raman spectroscopy. It was found that the concentration of SO42- in pore water samples decreases as the depth increases, while the expected Raman signal of methane has not been observed. A possible reason for this is that the methane escaped after sampling and the remaining concentration of methane is too low to be detected. To find more effective ways to analyze the composition of pore water, two novel approaches are proposed. One is based on Liquid Core Optical Fiber (LCOF) for detection of SO42-. The other one is an enrichment process for the detection of CH4. With the aid of LCOF, the Raman signal of SO42- is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup. The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water. By CCl4 extraction, methane at a concentration below 1.14 mmol/L has been detected by conventional Raman spectroscopy. All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO42- and CH4 detection in pore water.

20.
Anal Chem ; 87(9): 4788-96, 2015 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-25821993

RESUMO

Laser ablation molecular isotopic spectrometry (LAMIS) for rapid isotopic analysis of zirconium at atmospheric pressure was studied with a femtosecond-laser system operated under high repetition rate (1 kHz) and low pulse energy (160 µJ). The temporal evolution of zirconium neutral-atomic and ionic lines, as well as zirconium oxide molecular bands, were studied. Six molecular bands, belonging to the d(3)Δ-a(3)Δ (i.e., the α system) and E(1)Σ(+)-X(1)Σ(+) transitions, were observed with appreciable isotopic shifts. The assignments of the isotopic bandheads were first based on theoretical predictions of the band origins and the associated isotopic shifts of various dipole-allowed ZrO electronic transitions, followed by an experimental confirmation with a (94)Zr-enriched ZrO2 sample. In this work, the α(0,1) band from the d(3)Δ3-a(3)Δ3 subsystem was utilized for Zr isotope analysis based on a compromise between the magnitude of isotopic shifts in emission wavelengths, emission strengths, signal-to-background ratios, and spectral interferences. The analysis was performed in a standardless calibration approach; the isotopic information was extracted from the experimentally measured molecular spectra through theoretical spectral fitting. The results demonstrate the feasibility to obtain isotopic information for a spectrally complicated element like zirconium, without the need to use isotopically labeled calibration standards. The availability of comprehensive molecular constants will further improve the analytical accuracy of this standardless calibration approach.

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